Workaround for GCC -Wduplicated-branches, again

[mjanzen]

I see that Issue 573 fixed a duplicated-branches warning from gcc 7.1, back in 2017. I'm trying out fmtlib 7.0.3 with gcc 7.5.0, and am running into a similar duplicated-branches warning.

The fmtlib code has moved around since then, but following the example in commit bef89db I was able to add the same workaround to fmtlib 7.0.3 by changing 1 to +1 in fmt/core.h in lines 913 and 925.

[mjanzen]

I don't have permission to do a pull request, but here's a quick patch:

fmtlib.1912.patch.txt

[vitaut]

Added a workaround in #1914. Thanks for reporting.